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| Report on the circumstances leading to the 1996 outbreak of infection with E.coli 0157 in Central Scotland, the implications for food safety and the lessons to be learned. |
| Chapter 10 Surveillance |
| 10.1 An outbreak of infection of foodborne illness may be defined either as 2 or more linked cases of the same illness, or as the situation when the observed number of cases unaccountably exceeds the expected number. |
| 10.2 An essential part of any programme for the control of outbreaks of illness is the recognition of a change in the distribution of illness. To this end surveillance, ie the collection, collation, analysis and dissemination of information, is a vital tool. Three sources of data are important in the surveillance of foodborne diseases - the notification system, laboratory testing and reporting, and information on outbreak investigations. Surveillance is carried out at a local, national and international level. |
| 10.3 The best surveillance system in the world cannot prevent outbreaks. However, early identification of an outbreak is an important element in aiding the investigation and management of the outbreak and in helping to ensure that it can be brought under control as swiftly as possible. Surveillance can help inform appropriate research and aid understanding of the epidemiology of infection, leading to improvements in the understanding of the organisms involved, the factors influencing outbreaks and the spread of infection and the most appropriate means to manage and control future outbreaks. In addition, sound surveillance data can inform policy decisions and form the basis for legislative change. All of this is, clearly, particularly important in the case of an organism of the nature and virulence of E.coli O157, about which much remains to be learned. |
| Interim Report and Priority Recommendations |
| 10.4 We have
acknowledged that the laboratory surveillance of the
organisms responsible for foodborne infectious intestinal
disease in Scotland is amongst the best in the world.
Nonetheless, we recognise the need to build upon that
system, taking account of lessons learned, to bring about
further improvements in the surveillance and reporting
arrangements. We therefore recommended in our interim
report:- a. that the Management Executive of The Scottish Office Department of Health (SODoH) should consider urgently the practicalities, costs and benefits of introducing, through contractual arrangements, improvements to surveillance and data collection and analysis; b. that SODoH should review the current statutory and non-statutory mechanisms for the reporting of food poisoning and the organisms causing it; and c. that the Scottish Centre for Infection and Environmental Health (SCIEH) should produce, with the Scottish laboratories, the Scottish Consultants in Public Health Medicine (Communicable Disease/Environmental Health) Group and others as appropriate, costed proposals to permit timely electronic reporting and analysis of data and that they should be submitted to The Scottish Office for funding approval. |
| We also stressed the need for full and prompt clinical, epidemiological and laboratory investigation of outbreaks and liaison between the range of bodies involved. |
| 10.5 We are aware that discussions have been held between SCIEH and appropriate colleagues both north and south of the Border about the introduction of an electronic laboratory data reporting and collection system. We understand SCIEH's preferred option is to introduce CO-SURV, a software system which, if introduced, will mean that the data collection system in Scotland is compatible with that in operation in other parts of the UK. We understand work is now in hand to establish a multi-disciplinary steering group to oversee the detailed design of the system, in collaboration with all relevant interests. This is an essential step in bringing forward comprehensive, fully costed, proposals and we welcome that. |
| 10.6 We also understand that the non-statutory system for the reporting, to SCIEH and local CsPHM by laboratories, of a specified list of organisms isolated, has been reviewed. The list of organisms to be reported has been adjusted accordingly and the revised list is to be circulated for consultation amongst relevant interested professional groups. Once this list is agreed, following the consultation period, the SODoH Management Executive intends to write to all Scottish microbiology laboratories, requiring them to report isolation of the organisms on the specified list to SCIEH and the local CPHM. Again, that is very welcome. |
| 10.7 We also recommended earlier that SODoH should review the statutory notification system for foodborne illness. We are pleased that initial discussions on this have commenced with appropriate colleagues north and south of the Border. At the same time, however, we recognise that the notification system is an integral part of infectious disease legislation in Scotland and that any modification would require legislative change. Against that background, we consider that the best course of action would be to review the notification system as part of a more general review of the infectious disease legislation in Scotland. Again we welcome the prompt action that has been taken in response to our priority recommendations. |
| Further Consideration |
| 10.8 In our further deliberations, we have identified a number of additional issues on which we wish to comment. In broad terms, these relate to selective testing policies in laboratories; practices and techniques for the identification of E.coli O157; associated issues about case definitions; and issues about capacity and expertise within the laboratory network system in Scotland. |
| Selective Testing Policies in Laboratories |
| 10.9 The 1995 ACMSF Report recommended that all UK laboratories should examine all stools for E.coli O157. In our interim report (at Annex A), we proposed testing by all diagnostic laboratories in Scotland of all faecal samples from people with diarrhoea for E.coli O157 and reporting arrangements related to that. |
| 10.10 Evidence we have received suggests these recommendations are not being uniformly heeded. The reasons for this are, to an extent, understandable: more limited testing may be sufficient for clinical management purposes and laboratories may be selective about the testing of faecal samples and the tests used for financial reasons. The costs of testing in an outbreak of the scale of that in Central Scotland, for example, highlights the difficulty for authorities of fulfilling the requirements suggested by the ACMSF. |
| 10.11 We accept that regard has to be given to the cost implications of any proposal to extend diagnosis and surveillance. A sensible approach, and consistency of approach between Health Board areas in Scotland, needs to be promoted. |
| Testing Techniques and Practices |
| 10.12 Similar arguments can be advanced in relation to testing techniques and practices, especially as new techniques are developed. Different techniques may be employed, leading to inconsistency in results. We would like to see a standardised approach adopted - for example initial testing with a selective indicator medium, with immuno magnetic separation also used for those with indicative symptoms if the initial test is negative, followed by submission of isolates to the reference laboratory for phage typing and pulsed field gel electrophoresis to identify the strain of the organism. A prescriptive approach, however, seems inadvisable - not least because the state of the science is continually moving on. |
| 10.13 We also highlighted earlier the critical need for good and early contact between all of those concerned in actual or potential outbreaks. In that context, we stress the need for positive results from testing to be reported by laboratories immediately to the local Consultant in Public Health Medicine (CD/EH). |
| Case Definitions |
| 10.14 Allied to the issue of testing techniques and practices, and a problem which has arisen in the context of recent outbreaks, is the matter of case definitions. Essentially, faecal samples can show positive or negative results. A positive result indicates current infection with excretion of the organism - implying no need for serological testing. Individuals with negative tests on faecal samples can however have positive results on serological testing, implying exposure to the organism in the recent past. The question, therefore, of whether faecal negative but serological positive cases should be included in outbreak data has to be addressed. |
| 10.15 Our view is that cases showing positive results from serological testing only should not be included as cases in publicly reported outbreak statistics (although they are of interest and relevance to analytical epidemiology and SCIEH is giving consideration to their relevance to national surveillance). We suggest the need for a standard approach to avoid confusion and potentially inappropriate outbreak management and control measures. We suggest that the working party established to review the Guidance on the Investigation and Control of Foodborne Disease in Scotland should address the issue of case definitions in the light of the problems that have arisen in the Central Scotland outbreak. |
| Capacity and Expertise Within the Laboratory Network in Scotland |
| 10.16 Unlike south of the Border, Scotland has an informal network of public health laboratories based in NHS Trusts and no central funding arrangements for the routine testing of food or clinical samples. Although public health laboratories have considerable expertise in the routine testing of food and clinical samples, the ad hoc nature of their local contractual arrangements leaves them vulnerable to reductions in funding. The Reference Laboratories for those organisms commonly associated with food poisoning, such as E.coli O157, are however centrally funded. |
| 10.17 We heard concerns that at least some NHS laboratories and private laboratories may not find it commercially viable to provide the resources and expertise to carry out the sophisticated testing required for identifying E.coli O157, for example. Some concerns were expressed about the robustness of microbiological results obtained from laboratories which may not be as rigorously quality assured as NHS laboratories. Commercial competition for testing and generally reduced levels of expenditure on testing by local authorities may mean that it is difficult for NHS laboratories to maintain a critical mass of work and expertise. Financial pressures mean that the NHS laboratories in some Health Board areas may restrict their work to clinical samples and discontinue food and public health testing thus losing expertise in this field. Financial pressures on laboratories are also likely to increase as a result of the need for independent third party accreditation, by November 1998, for laboratories testing food and the costs associated with that. It is important that any future review of laboratory services in Scotland addresses these issues. |
| 10.18 In the case of a large outbreak of foodborne infection like that in Central Scotland, however, rather different factors come into play. There is a need for laboratory facilities to be able to cope with a potentially very substantial increase in demand for human, food and environmental testing and, at the same time, for very prompt turn-around times for tests to aid outbreak management and control and meet legal requirements. In the case of the E.coli O157 reference laboratory in Aberdeen, for example, the Central Scotland outbreak has required the conversion of part-time staff to full-time; additional staff to be drafted in; many hundreds of hours overtime to be worked; and other reference work being put on hold. There have, therefore, been substantial additional and opportunity costs involved and the existing systems have been stretched to the limit. |
| 10.19 Finally, although non-O157 VTEC have not been causally implicated in any of the outbreaks we examined, we think it unwise to ignore their possible clinical importance. We endorse, therefore, the ACMSF recommendation that the Government should continue to support reference laboratory facilities for these organisms in order to maximise epidemiological information. |
| Recommendations |
| 10.20 We
recognise that some of these issues are unlikely to be
easily resolved and that work and consultations are still
underway on some of our earlier recommendations. Account
needs to be taken of the outcomes of that. Nonetheless,
we believe some measures can be taken to respond to the
issues we have identified and we recommend:- a. that SODoH should take steps to improve the implementation and monitoring of the recommendations of the ACMSF and this Group on laboratory testing of stool specimens. SODoH should consider whether there are any funding implications of the proposed testing arrangements; and b. that, in discussion with relevant professional groups, a standard case definition and a standard protocol should be agreed for testing and defining clinical cases of infection with E.coli O157 and their use promoted in all suspected E.coli O157 food poisoning investigations. |
| 10.21 Issues related to outbreak management and control are discussed later in this report. We suggest, however, that The Scottish Office and local authorities/Health Boards should ensure that consideration is given to the availability of sufficient laboratory facilities, surveillance capacity and personnel with appropriate expertise in drawing up local outbreak control plans. |
| The Need for Summary and Detailed Reports |
| 10.22 On a
more general issue, we found it extremely helpful to be
able to draw on the expertise and experiences of others
who had been involved in recent outbreaks; and to take
account, in reaching our conclusions, of other available
information and reports. It was also noted however that
the information available to SCIEH and others is
incomplete - full reports, and even minimum data sets,
are not available for all outbreaks. Infection with E.coli
O157 is a growing, global threat and information and
experience needs to be shared to improve awareness and
understanding of the organism and its epidemiology.
Lessons learned and knowledge gained need to be
disseminated. We therefore also recommend: a. that, on completion of investigations, it should be the responsibility of the CPHM to provide SCIEH with a minimum data set (in the form of a standard proforma) for all general outbreaks of infectious intestinal disease, including food poisoning; b. that for large (or otherwise significant) outbreaks a full, written report should be completed and consideration given to its publication. Copies of written reports should go to SCIEH; and c. in particular, there should be written, and published, a full report of the Central Scotland outbreak. |
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